Over the past several decades, various highly toxic chemical agents including chemical warfare agents (CWAs) have been developed and stockpiled by several nations. In January 1993, representatives from more than 130 nations signed the final draft of the Chemical Weapons Convention (CWC), which outlaws the production, use, sale, and stockpiling of all chemical weapons and their means of delivery and calls for the destruction of existing stocks. The CWC entered into force in April 1997. Out of an estimated 74,000 tons of CWAs contained in bulk storage vessels, metal barrels, canisters, rockets, landmines, mortar and artillery shells, cartridges, and missiles in the United States, former Soviet Union, and other countries about 24,000 tons have been destroyed as of July 2007 (www.opcw.org). While significant progress has been made, much work remains to be done. None of the countries met the original deadline and all have received extensions. The cost of disposal and objections from environmental groups to some of the technologies currently used for disposal remain barriers to the speedy disposal of CWAs.
The major CWAs fall into three main classes: sulfur mustards (HD and N), nitrogen mustards (HN1, HN2 and HN3), and organophosphorous nerve agents (acetylcholinesterase inhibitors) of the G (GA, GB, GD, GE, GF) and V (VX, VE, VG, VM) type. Additionally, lewisite (L) and adamsite have been produced in significant quantities.
It was decided by appropriate authorities that the method of choice in the United States for the disposal of chemical stockpiles would be by incineration because of the perceived low cost and the relative simplicity of incineration technology. However, it is becoming clear that incineration of chemical warfare agents poses risks of both an immediate and long term nature which may not be acceptable to the public. Public health and ecosystem integrity are threatened by the emission of materials which can escape the combustion train, resulting in uncharacterized products of incomplete combustion which are dispersed into the atmosphere. Less than 72 hours after start-up, the U.S. Army had to shut down its first domestic CWA destruction facility in Tooele, Utah, located in a sparsely populated region in the western United States, when the nerve agent Sarin was detected in an area outside the chamber in which Sarin-filled rockets were being destroyed.
Earlier public opposition to incineration led U.S. government authorities to consider alternative methods, including chemical treatment of the CWAs, capable of producing environmentally benign products. However, this concept was dismissed in the United States after publication in 1984 of a National Research Council report stating that, when compared to incineration, chemical neutralization processes “are slow, complicated, produce excessive quantities of waste that cannot be certified to be free of agent, and would require higher capital and operating cost.” However, recently some of the chemical treatment methods such as neutralization with an alkali metal hydroxide have been used for detoxifying chemical weapons such as VX nerve gas.
Alternatives to incineration such as molten salt oxidation, supercritical water oxidation, reactions with various chemicals, electrochemical oxidation, neutralization, hydrolysis, biodegradation, steam-reforming, etc., have been proposed in the literature. This is not an exhaustive list. However, it does give an indication of the methods that have been proposed.
The chemical treatments proposed in the past for detoxifying chemical warfare agents have not been entirely satisfactory. For example, the treatments have not been applicable to the entire spectrum of chemical warfare agents. Most chemical reagents are species-specific; that is, a chemical reagent generally reacts with a substance having a certain specific functional group. With such species-specific chemistry, destruction of a CWA would require one to first establish the identity of the CWA or the mixture of CWAs to be destroyed in order to select the right reagent or combination of reagents to react with that particular material.
Chemical methods previously proposed for the destruction of chemical warfare agents are also believed to require unacceptable capital and labor costs. In view of this background, it is easy to understand that compared against such chemical treatments, incineration of the CWAs to produce water, carbon dioxide and inorganic salts, appears attractive. However, as discussed earlier, incineration has its own problems due to release of undesirable byproducts and other safety issues. This has led to a significant public opposition to incineration.
The need therefore exists for a treatment system that does not employ chemicals or equipment that are difficult or dangerous to transport. Unfortunately, existing chemical treatments for detoxification of chemical agents have significant drawbacks. Existing detoxification solutions are only effective against a certain class of agents. Also, use of existing decontaminants under inappropriate conditions can result in the formation of dangerous by-products.
Most chemical detoxification processes include some form of hydrolysis. Hydrolysis is accomplished by reacting CWAs with a base such as an alkali metal hydroxide. Hydrolysates are the reaction products of the reaction between the chemical agents and the base. Hydrolysis of CWAs creates intermediates or oxidation by-products of CWAs such as organophosphorous compounds that are sometimes more toxic than the agent itself. While hydrolysis may be acceptable for some organophosphorous compounds, it is not universally effective against all or even most CWAs.
These considerations highlight the need for a system capable of detoxifying a broad range of chemical warfare agents without producing toxic by-products. In addition, there is a need for a detoxification system that is compatible with most common materials, easy to dispense and environmentally safe. The present invention provides a simple and efficient method for achieving these objectives.